Effects of surfactant on the structural and magnetic properties of hydrothermally synthesized NiFe2O4 nanoparticles

A simple and effective hydrothermal route is adopted where glycerol and NaOH are used as surfactant and precipitating agents respectively, for the synthesis of NiFe2O4 (NFO) magnetic nanoparticles. The structure and morphology of the as prepared NFO are characterized by X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM) techniques. The formation of phase-pure NFO is evident from the XRD studies. The crystallite size calculated using the Scherer equation are in the range of 22-38 nm. A mixed morphology of spherical and octahedral shape are found in FESEM images depending on the concentrations of glycerol as surfactant. The increase in Curie temperature (T-c) from 805 to 815 K is observed, when the surfactant concentration is increased from 10 to 20% w/v. However with an increase in surfactant concentration to 40% w/v, the T-c decreases to 790 K. The NFO nanoparticles prepared at 10% w/v surfactant concentration show a high saturation magnetization (M-s)of 42 emu/g which increases to 53 emu/g at 20% w/v of surfactant. Very small change in M-r (decrease of 1-2 emu/g) is noticed with further increase in surfactant to 40% w/v. The possible explanations are hypothesized for such observed phenomena. A linear dependence of coercivity (H-c) and remanence (M-r) with surfactant concentrations is found for NFO nanoparticles, where both H-c and M-r decrease with increase in surfactant concentrations. It is found that glycerol, which is economical and eco-friendly, is an effective surfactant to prepare NFO nanoparticles with desirable magnetic properties and controllable particle size.